The invention relates to a method for removing scum in a drum washing machine and a drum washing machine suitable for this purpose. In particular, the invention relates to a method for removing scum in a tub of an electronically controlled drum washing machine, wherein, following a main washing cycle and an operation for pumping out the liquid, certain steps are carried out, and also a drum washing machine suitable for this purpose.
In a conventional drum washing machine, high-speed spinning takes place immediately after the main wash cycle and the rinse cycles. If an excessive amount of scum is present or is produced during spinning, the detergent-solution pump does not however pump the scum/detergent-solution mixture or at all events pumps it poorly. The spinning is therefore not performed when scum is detected during pumping out or in the event of scum being detected during the spinning operation. Early detection of scum is thus important in order to enable efficient measures to be taken to remove the scum.
According to DE 41 04 151 A1, the scum is destroyed by switching on a heating facility. In order to also destroy the scum in the extended surrounding area of the heating facility, the drum is rotated slowly such that further scum reaches the heating facility where it is destroyed by the application of heat.
A facility for destroying detergent scum is described in DE 43 34 969 A1, which has a device for generating hot air that is introduced between the tub and the drum by means of a feed pipe in the tub wall.
In addition, methods for removing scum in a tub of a drum washing machine are known from DE 102 34 472 A1 and also from DE 198 46 248 A1.
DE 102 34 472 A1 thus describes a method for removing scum in a tub of an electronically controlled drum washing machine as a result of a program step which is provided for draining the tub, having a detergent-solution runoff system arranged on the base of the tub which has a detergent-solution pump and a sensor for determining the level of liquid contained in the tub. The waveform of the sensor signal (P) which is recorded during operation of the detergent-solution pump contains a gradient Δpn/Δtn, in comparison with Δpn-1/Δtn-1, which indicates the presence of scum, whereupon a scum handling measure matched to the gradient is then initiated.
As described in EP 0 278 239 A1, excessive scum formation in the main washing cycle, which can be observed while the washing detergent solution is being heated in the tub, is removed by the addition of a limited quantity of cold water and/or by temporarily switching off the detergent solution heating.